The present invention relates to a plate type gas to gas heat exchanger and more particularly it relates to a plate type heat exchanger having a plurality of thin rectangular plates which is simply constructed and efficient in operation. The invention is particularly suited for but not limited to the exchange of heat between process flue gas and an incoming process gas such as combustion air. As is well known the exchange of heat between a cold stream entering a process and a hot stream leaving a process leads to a reduction in the total energy requirement of the process. Hence, it is common practice on furnaces, incinerators and the like to preheat incoming combustion air, thereby increasing the process efficiency. Heretofore various types of gas to gas heat exchangers have been used in this connection.
A conventional plate type heat exchanger used for heat recovery from gas streams generally consists of a plurality of plates which are made of thick metal material so as to withstand the pressure difference between the two streams and possible corrosion effects. In order to reduce the bulk size of such an exchanger the heat exchange plates are provided with fins which are welded to the plates or formed with the plates by casting. Since finning adds considerable weight to the heat exchange plates these exchangers are heavy and of considerable bulk. In the patent by W. F. Hart, U.S. Pat. No. 4,029,146, an attempt was made to overcome these disadvantages by forming the heat exchange plates out of corrugated thin metal sheets which are mounted in a packing and are pressed together by the pressure difference between the two streams. The corrugation rims on two adjacent plates serve to separate the plates against the pressure difference between the two streams, but in the same time the corrugation rims form narrow channels through which the two fluids must flow. In furnace heat recovery applications, this arrangement presents the disadvantage that the narrow channels can become clogged by soot deposition from the combustion gases thus impairing the proper functioning of the exchanger. The heat exchanger of the present invention overcomes the above mentioned difficulties by attaching to each plate, by rivets, spotwelding, or any other method, a series of reinforcing strips which serve to maintain the separation of the plates against the pressure difference of the two streams, at the same time providing wide channels through which gas can flow. The present invention also prevents a method for the easy realization of a thin plate exchanger by folding the plate sides in such manner as to allow for the sealing of the two streams from each other and to provide external gasket sealing and flange mounting surfaces.